Wear on the flanges and treads of railway wheel is a well-known phenomenon, with the wear giving rise to increased operating costs and reduced safety if the presence of the defect is not quickly established so that the carriage in question can be taken out of service and be repaired at a time expedient for railway operations.
Usually, the presence of wear on railway wheels is ascertained by manual inspection of the treads and flanges of the wheels. This is a difficult procedure to control, and there are also purely practical difficulties in mechanically measuring and checking the wheel profile.
Today, the maintenance of the wheels is almost never effected on the basis of a conditional supervision but on the basis of statistical empirical data, with the result being that some wheels with defects are not discovered and immediately repaired, while, on the other hand, many failure-free wheels are subjected to unnecessary inspection. However, it is known that the wear on treads and flanges can occur far more quickly than expected, for example, because of insufficient rail lubrication or following track repair work. Wheels with worn treads or flanges must, however, be repaired as quickly as possible after the defect has been ascertained, in that these wheel defects can result in greatly increased wear and further possible damage. Moreover, worn wheels increase the possibility of derailment, particularly when running in curves and through switch points.
In for example, PCT/DK87/00122, an apparatus for the scanning of the wheel profile on passing train wheels is proposed which is based on the wheel intersecting a skewed beam of light or pencil of rays during the simultaneous measurement of the distance to the reflection point(s) on the running surface. In practice, this apparatus functions as desired, but requires a measurement of the speed of the wheel in order to provide precise information concerning the wheel profile.
European patent application no. 0,228,500 proposes an apparatus for contact-less measurement of the wherein the wheel profile is illuminated from underneath with a light edge. The scanning of the wheel profile is effected tangentially to the wheel with one or more cameras, the signals from which are processed electronically. This apparatus can only function with the use of a narrow auxiliary rail, so that almost all of the wheel profile can be illuminated from underneath, and, consequently, the apparatus can only be used during very slow running of the train wheel and with unloaded carriages or in workshops where the wheels are lifted free of the rail element.
In German publication no. 3,526,923, an apparatus for the measuring of wheel profiles is proposed wherein a skewed laser beam is intersected by a wheel as it passes, and, at the same time, a camera photographs the illuminated area. The resulting photographs of the wheel profile are compared with pictures of correct wheels taken at the same angle. As apparent such an apparatus can provide only a very rough picture of the extent of the wear on a wheel, and it can be assumed that the apparatus can only be used to find very severe damages on the wheels.